Doppler radars



Jan. 21 1969 J. c. PRETI 3,423,753

DOPPLER RADARS Filed March 21, 1967 3,423,753 DOPPLER RADARS Jean Claude Preti, Clamart, France, assignor to Societe de Fabrication dlnstruments de Mesure (S.F.I.M.),

Massy (Essonne), France Filed Mar. 21, 1967, Ser. No. 624,770 Claims priority application9 France, Sept. 16, 1966,

U.S. Cl. 343-s Int. Cl. G01s 9/44 4 Claims ABSTRACT OF THE DISCLOSURE An object of the present invention is to provide improvements in microwave circuits of detection and ranging devices, more especially in doppler radars.

This invention relates in improvements to the microwave circuits of detection and ranging devices known as doppler radars, primarily with a view to confining such circuits solely to the Klystron Reflex type transmitting tube and the associated antenna, by picking up the information produced by the doppler efiect in the form of a beat set up within the cavity of the Klystron tube between the transmission frequency and the frequency received after reflection from a moving target.

In accordance with a first improvement, such a Klystron reflex tube comprises, in its cavity circuit or in its cathode circuit, a feed circuit embodying a resistor and an information pickup device, and is associated with an adjust-able waveguide.

In accordance with another improvement, said resistor has a resistance of about 300 ohms.

In accordance with another improvement, the Klystron tube oscillates on its 5% mode, i.e. with a bias included between --200 and 250 volts in the case of a type 2K25 tube, for which the cavity voltage is of course 300 volts.

Such provisions ensure a high degree of efliciency in the mixing of the transmitted and reflected signals and in the picking up of the resulting doppler signal.

The description which follows with reference to the accompanying non-limitative exemplary drawing will give a clear understanding of how the invention can be carried into practice.

In the drawing:

FIGURE 1 shows schematically the association of a Klystron mixer tube and an antenna in a doppler radar.

FIGURE 2 is a top view of the waveguide; and

FIGURE 3 is a circuit diagram for a Klystron tube.

Reference is first had to FIGURE 1, in which a Klystron tube 1 and its antenna are secured in association with a waveguide 3, with penetration of a sight vane thereinto. The exit end of waveguide 3 is equipped with a reflector 4 facing a parabolic mirror 5, the rear part of Klystron tube 1 being occupied by an adjustment piston 6 carried on the end of a threaded rod 7 with which cooperates a knurled adjustment knob 8 which is rotably mounted in nited States Patent a gland 9 on the end of waveguide 3 without being able to move axially.

In the electrical circuitry of such a Klystron tube, the circuit of cathode 10 is grounded through a resistor 11 having a rated value about 300 ohms, an information pickup line 12 being connected between cathode 10 and resistor 11 so as to convey this information to a suitable amplifier and thence to the ultimate utilization means.

Klystron 1 is caused to operate on its 5% mode by imparting to it a bias between -200 and 250 volts (should the Klystron be a type 2K25 tube), the cavity voltage naturally being 300 volts.

In order to obtain a maximum from the doppler signal issuing from circuit 12, the position of piston 6 must be precisely adjusted so as to obtain optimum mixer efliciency. Such adjustment can be accomplished, for example, by seeking the maximum doppler signal that can be picked up when the parabolic mirror 5 is aimed at an imaginary target such as a rotating corner reflector.

Obviously, should the transmitting frequency of the Klystron tube vary, or should this tube be replaced, the position of piston 6 must be readjusted.

It goes without saying that changes may be made to the form of embodiment hereinbefore described without departing from the scope of the invention.

What is claimed is:

1. In a doppler radar transmitter-receiver, in combination, a waveguide, a Reflex Klystron tube having a sight vane projecting into said waveguide, a cathode resistor in the electrical circuitry of said Klystron tube, and information-representing voltage pickup means electrically connected directly to said cathode resistor, whereby the doppler effect is produced in the form of a beat frequency within the cavity of said Klystron tube between the Klystron pulse transmitting frequency and the frequency of reception of those pulses following reflection thereof off from a moving target, said beat frequency being conveyed directly to said pickup means, whereby the electronic section of said transmitter-receiver is restricted to said Klystron Reflex tube.

2. In a transmitter-receiver as claimed in claim 1, wherein said cathode resistor has a rated value of about 300 ohms.

3. In a transmitter-receiver as claimed in claim 1, a Klystron bias voltage included substantially between 200 and -250 volts for an anode voltage of about 300 volts, the whole within a type 2K25 Klystron tube, whereby said tube operates on its 5% mode.

4. In a transmitter-receiver as claimed in claim 1, a reflector at the first exit end of said waveguide, a parabolic mirror, said reflector facing said parabolic mirror and located at the focal point thereof, and a piston for adjusting the length of said waveguide, said piston being located at the end of said waveguide remote from said first end.

References Cited UNITED STATES PATENTS 2,406,370 8/1946 Hansen et al. 10270.2 2,406,371 8/1946 Hansen et al. 32519 X 2,596,996 5/1952 Hansen et al. 3438 RODNEY D. BENNETT, Primary Examiner.

CHARLES L. WHITHAM, Assistant Examiner.

U.S. Cl. X.R. 

